1. Field of the Invention
This invention relates to an interchangeable-lens type camera system and more particularly to a system called an electronic mount system which performs data communication between a lens unit and a camera body.
2. Description of the Related Art
The electronic mount system has never been arranged to have units of the same function connected to the two ends of its data communication channel.
For example, an automatic focusing (hereinafter referred to as "AF") device, the interchangeable-lens type camera system is arranged to have the AF device connected to only one of the two ends of the data communication channel. The AF device is never disposed on both the lens unit side and the camera body side. An example wherein an infrared ray type AF device is completely set only within the lens unit is arranged as described below with reference to FIG. 1 of the accompanying drawings:
An infrared ray projector 102 projects infrared rays onto an object 101 to be photographed. This gives reflected rays, which are received by an infrared ray sensor 103. A judgement circuit 104 judges a focusing state of the lens 107 according to the output of the sensor 103. If the lens 107 is in focus, no correction is required. If not, the judgment circuit 104 supplies a driver 105 with a signal indicating the direction and degree of correction required according to a near focus or far-focus state as determined by the judgment circuit 104. In accordance with the output of the judgment circuit 104, the driver 105 produces a control signal. A motor 106 is driven by the control signal to shift the position of the lens 107 to an in-focus position. As a result, an image is formed in an in-focus state on an image sensor 203 which is disposed on the side of the camera body.
The examples of conventional AF arrangement include a TV-signal-using AF (hereinafter referred to as TV-AF) arrangement wherein the in-focus determining device is disposed on the side of the camera body as shown in FIG. 2. The TV-AF arrangement is as follows: A lens 107 forms, on an image sensor 203 disposed on the side of the camera body, an image of light coming from an object 101. As a result, a camera signal processing circuit 204 generates and outputs a TV signal. A high-pass filter 205 extracts from the output of the camera signal processing circuit 204 only a high-fineness signal which is obtainable in a large quantity under an in-focus condition. An analog-to-digital (A/D) converter 206 converts the high-fineness signal into a digital signal. The digital signal is used by an in-focus judgment circuit 207 for determining a focusing state.
Further, for finding the direction in which a defocusing state is obtained, an actuator 208 which is made of a bimorph plate or the like is driven by a driver 209 in accordance with a signal of a frequency which is several times as high as a frame frequency signal generated by a timing signal generator 210. The image sensor 203 is vibrated and moved to a minute extent back and forth from a focal plane to enable the in-focus judgment circuit 207 to make a discrimination between a near-focus state and a far-focus state. The result of discrimination is transmitted to a driver 105 which is disposed on the side of the lens unit. The driver 106 then shifts the position of the lens 107 to an in-focus position according to the result of discrimination.
The interchangeable-lens type camera system can be arranged without any problem with an in-focus judgment device disposed only on one of the lens unit side and the camera body side as described above. However, in the light of the latitude of system arrangement as a whole, the conventional system has lacked expansibility.